1. Field of the Invention
The present invention generally relates to an optical disc device. More specifically, the present invention relates to an optical disc device for reproducing an optical disc, and to an optical disc reproduction method.
2. Background Information
Optical discs such as CDs (compact discs), DVDs (digital versatile discs), and BDs (Blu-ray Discs™) have come into widespread use in recent years. Furthermore, optical disc devices have been developed as devices that read, record, and reproduce the information recorded on an optical disc, such as audio information or image information. Examples of well known optical disc devices include CD players, DVD players, BD recorders, and CD-ROM drives that are connected to a personal computer.
An optical disc device is equipped with an optical pickup for reading information by directing a laser beam at an optical disc. The optical pickup has a laser diode for directing the laser beam at the information recording face of the optical disc, which is fixed to and rotating on a turntable.
The optical pickup also has a photodetector, such as a photodiode, for receiving reflected light from the information recording face. The optical pickup converts light into an electrical signal by means of this photodetector, and outputs the resulting signal.
In order to read information accurately from an optical disc, tracking must be performed, in which the optical axis of the laser beam is made to track the center of pits formed on the optical disc. To do this, an actuator for driving an object lens in the radial direction of the optical disc, and a tracking servo for controlling the actuator are provided inside the optical pickup device.
To improve the quality of the signal from the optical pickup and to enhance servo performance in an optical disc device such as this, a technique has been employed in which a high-frequency signal is superposed over the drive signal of the laser diode that emits the laser beam.
In relation to this technique, an optical disc device has been disclosed and proposed in which disturbance of the signal from the optical pickup is detected, and the amplitude of the high-frequency signal superposed onto the drive signal (hereinafter referred to as the “high-frequency superposition amplitude”) is varied according to this detection result (see International Publication No. WO 2004/105006 (Patent Literature 1), for example).